This invention relates to battery charging devices, and in particular to a self-contained emergency battery charger for use in motor vehicles for charging a fully or partially discharged starter storage battery which delivers current to a starter motor of the vehicle.
A motor vehicle storage battery frequently falls into a state of discharge such that it cannot deliver sufficient current to the starter motor. This is often due to lights or other accessories being accidently left on. Also, defective vehicle charging systems can result in the same problem.
To start a vehicle whose storage battery has been partially or completely discharged requires either by-passing the electrical starting system entirely or supplying the electrical starting system with an additional source of external electrical power. The former technique is generally accomplished by push-starting the vehicle and the latter technique by using either jumper cables connected to a fully charged external power source in another vehicle, termed xe2x80x9cjump startingxe2x80x9d, or a conventional battery charger. Push starting requires assistance in the form of a push vehicle or human muscle power. Additionally, only cars fitted with standard transmissions can be push started. Jump starting requires the aid of an additional vehicle. Further, cables must be available and must be externally connected, requiring the user to exit the vehicle, and be exposed to the hazards of weather or of possible battery explosion and associated mishaps as a result of a misconnection of the cables. The disadvantage of a conventional battery charger is the need to be near a source of external power such as 120 volts alternating current.
To overcome these problems and the limitations of prior art attempts to solve the problem, such as being useful only for one or two battery charges before the secondary battery source must be replaced, a very slow recharge cycle, a need for an external source of power, and insufficient portability or lengthy charging/recharging times, assignee developed a battery booster, subsequently patented as U.S. Pat. No. 5,637,978, issued on Jun. 10, 1997, said patent being incorporated herein by reference and hereinafter referred to as the ""978 battery booster.
Through extensive testing of lead acid batteries Applicants have learned that a fully drained automotive (lead acid) battery will not accept current and return it efficiently under certain conditions. Specifically, Applicants have found that when a lead acid battery (originally a nominal 12 volts) is discharged below 5 volts, the charge acceptance is  less than 40%. The original design parameters for the ""978 battery booster were to deliver 5 amps constantly from the time the charging switch is activated. During testing, limited success was achieved starting vehicles. The ""978 battery booster, as originally designed was successful in starting vehicles whose discharged batteries were xe2x89xa79.5 volts. Further research verified that low current return occurred when the lead acid battery was  less than 5 volts. A very high rate of current return (88% to 92%) occurred when the lead acid battery was  greater than 10.5 volts.
During their research, Applicants also found a variation in time required to recharge a lead acid battery. Applicants found that, within operating temperature limits, during a given time period, a warm battery will provide more electrical power than cold battery. Therefore, under colder conditions the time required to fully recharge a battery is longer. The original ""978 battery booster had a simple resistor/capacitor circuit that took a resistor of fixed value and charged a capacitor of a fixed value giving a fixed time regardless of temperature.
The present invention xe2x80x9cpreconditionsxe2x80x9d a discharged battery before applying a full charging current from a charged second battery to the discharged battery. The invention circuitry first checks the voltage level of the discharged battery. If the voltage level is at or below a first predetermined level, a minimum charging current, which is less than half the value of a full charging current, is applied to the discharged battery from the second battery. The minimum charging current is applied to the discharged battery until the voltage of the discharged battery rises to a second predetermined level. After the voltage of the discharged battery reaches the second predetermined level, the invention applies a full charging current to until the discharged battery is fully charged.
In providing the charge to the discharged battery from the charged second battery, the present invention adjusts the time of charging whereby the time for providing power from the second battery is increased or decreased in relation to the second battery""s temperature.
These together with other objects of the invention, along with various features of novelty which characterize the invention, are pointed out with particularity in the claims annexed hereto and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and the specific objects attained by its uses, reference should be had to the accompanying drawings and descriptive matter in which there is illustrated a preferred embodiment of the invention.